The present invention relates to the production of concentrated HCl vapors, and, more particularly, to a method of producing concentrated HCl vapors from super-azeotropic solutions by means of direct heating.
Various technologies are known for producing concentrated HCl vapors from super-azeotropic solutions of HCl, including:                concentration by varying the operating pressure, and        concentration by extractive rectification (i.e., adding an extractive agent).        
With regard to processes utilizing a varying operating pressure, the concentration of HCl at the azeotrope point is known to depend on the operating pressure. Therefore, it is possible to concentrate the HCl by operating distinct stages employing two different pressures. The feed mixture is first subjected to low pressure to produce a mixture having an azeotropic composition. The mixture is then subjected to a higher pressure in a second stage. While a substantially azeotropic mixture is obtained in the second column, the aqueous HCl concentration is lower than the azeotropic composition of the first stage due to the higher operating pressure. Thus, the liquor from the second column may be recycled to the first column. Concentrated hydrochloric acid may be removed in the vapor phase from the second column.
In concentration by means of extractive rectification, the azeotrope point is suppressed by an extractive agent, so as to increase the relative volatility of the HCl. The extractive agent may be strongly hygroscopic. Hydrochloric acid of high concentration or HCl gas may be produced at the head of the extractive rectification column. Upon being introduced to an extraction column, the extraction agent extracts, and becomes diluted with, water from the HCl feed stream. Outside of the column, the extractive agent is reconcentrated and recycled to the extraction column.
The above-described processes notwithstanding, it is believed that there is a need for further improvements in methods and systems for producing concentrated HCl vapors from solution, and the subject matter of the present disclosure and claims is aimed at fulfilling this need.